Piezoelectric electromechanical transducer



June 11, 1963 R. R. TEN EYCK 3,093,710

PIEZOELFCTRIC ELECTROMEZCHANICAL TRANSDUCER Filed July 6, 1959 2Sheets-Sheet l INVENTOR. RoBERT R TEN EYCK xwwam FITTOENEY June 11, 1963R. R. TEN EYCK PIEZOELECTRIC ELECTROMECHANICAL TRANSDUCER Filed July 6,1959 2 Sheets-Sheet 2 TATE- T51 l E].

INVENTOR. ROBERT P. TEN EYCK 47 7 0 ENEY United States atent 3,093,710PIEZOELECTRIC ELECTROMECHANICAL TRANSDUCER Robert R. Ten, Eyck,Metuchen, N.J., assignor to Gniton Industries, Inc., Metuchen, N.J., acorporation of New Jersey Filed July 6, 1959, Ser. No. 825,361 16Claims. (Cl. 179-110) This application is a continuation-in-part of myapplication Serial Number 803,524, filed April 1, 1959 now abandoned.

My invention relates to electromechanical devices and in particular tothose devices which require a reasonably fiat frequency response overthe audible range. More particularly, my invention is directed towardproviding an electromechanically sensitive ceramic transducer fordriving such devices. While I shall describe my invention in terms ofdriving a loudspeaker with such a transducer, it should be clearlyunderstood that the transducers of my invention may be used for drivingany electromechanical devices such as meters, servo valves, recordcutters (both stereo and monaural), and relays.

In the prior art there have been many attempts to produce loudspeakerswhich were driven by ceramic transducers. However, all of them lackedlow frequency response and as a result their use was confined to thehigh frequency element in multispeaker arrays. Since the use of 'apiezoelectrically driven loudspeaker will eliminate the need for anoutput transformer, there is a definite demand for such a speaker with afuller frequency range.

Accordingly, it is an important object of my invention to provide anelectromechanical device driven by a piezoelectric ceramic transducerwhich possesses a reasonably flat frequency response over the audiblerange.

It is a further object of my invention to provide a loudspeaker with theforegoing properties which is simple to fabricate and produce.

It is a still further object of my invention to provide a ceramictransducer capable of driving such a device.

These and other objects, features and advantages of my invention'will beapparent during the course of the following description when taken inconjunction with accompanying drawings wherein:

FIGURE 1 is a schematic diagram of a preferred output circuit used inconjunction with loudspeakers of my invention,

FIGURE 2 is an'elevational view of a preferred embodiment of myinvention showing the connection of the driving transducer to thediaphragm,

FIGURE 3 is a plan view of the transducer of FIG- URE 2,

FIGURE 4 is an elevational view of the transducer of FIGURE 3,

FIGURE 5 is a view similar to FIGURE 3 showing a transducer wherein onlya portion of each of the outer surfaces is covered by an electrode,

FIGURE 6 is a view similar to FIGURE 3 showing a transducer to the uppersurface of which there is aflixed a second transducer, F

FIGURE 7 is a view similar to FIGURE 4 showing a second transducerbonded to the upper surface of the transducer of FIGURE 3,

FIGURE 8 is a view similar to FIGURE 4 showing an electromechanicallyinert thin strip bonded to the upper surface of the transducer of FIGURE3,

FIGURE 9 is a View similar to FIGURE 3 wherein a plurality of thin cutshave been made in the upper surface of the transducer of FIGURE 3,

FIGURE 10 is a View similar to FIGURE 3 wherein an electromechanicallyinert element is mounted edgewise on the transducer of FIGURE 5, and

FIGURE 11 is a view similar to FIGURE 4 of the assembly of FIGURE 10.

In the drawings, wherein, for the purpose of illustration, are shownpreferred embodiments of the loudspeaker of my invention, the numeral 26designates the loudspeaker generally. Loudspeaker Ztl is fed fromamplifier 22 which comprises push-pull electron tubes 24a and 24b, inputtransformer 26, output inductor 23 and isolating capacitors Stla and 3%.Capacitors 30a and 3% may be dispensed with, as shown by the dottedlines in FIGURE 1, but under such conditions the plate voltage appearson the transducer of loudspeaker 2t and presents some shock hazard tothe user of the equipment.

Loudspeaker 29 (FIGURE 2) is seen to comprise frame 32, diaphragm 34,transducer 36, transducer clamp 38, driving pin 3, mounting plate es,mounting strut 42 and mounting frame 44. Clamp 3%; is held to mountingplate 4.0 by means of screws 4-1 and an insulator 39 of polyethyleneplastic or similar material is placed between the transducer and theclamp and another is placed between the transducer and the mountingplate to obtain electrical isolation of the transducer from the mountingassembly. Frame 32 is sometimes referred to as the basket and diaphragm34 is often referred to as the cone. It should be noted, however, thatdiaphragm 34 in loudspeakers of my invention need not be circular in theplane at which it is joined to frame 32. Any other shape such asellipses, polygons or any other closed figure may be used equallyeffectively. The diaphragm must be tapered so that its widest opening isin the plane at which it is joined to the frame.

I have found it best to fashion transducer 36 in the form of a ceramicsandwich wherein there are two ceramic thin strips 50 and 52 bondedtogether with a thin brass shim 54 between them in a manner well-knownin the art. Electrodes 56 and 58 are suitably affixed to strips 50 and52 in any manner Well-known in the art such as by reduction,electrodeposi-tion or other means. Driving pin 37 is atfixed totransducer 36 and to diaphragm 34 by bonding cement such as the radioservice cement factured by General Cement Co. Clamp 38 is preferablymade of steel and is afixed to mounting plate 40, which is made ofbrass, by means of screws 41, as shown in the figures. I choose to makeclamp 38 of angle iron to achieve greater rigidity and to eliminate thebowing which is present when a fiat, thin piece is used for the clamp.However, if a heavy enough material which will not bow or buckle underpressure of the bolts, is used, angle iron is unnecessary. Mounting stud42 and mounting frame 44 serve to anchor clamp 38 so that there is nomechanical interaction between the frame and the diaphragm.

I have found that I obtain good frequency response using loudspeakers ofmy invention when the transducer is formed of lead titanate-Zirconateand has the following dimensions:

Length: 3%" to 4 /2" Width: /8" to /8 Thickness of each ceramic elementof the sandwich:

I have also found that I can obtain equally good results if pin 37 islocated at positions along the longitudinal dimension of transducer 36'so long as it is at least halfway between clamp 38 and the free end oftransducer 36. Moreover, I have found it best to have some overhang ofthe transducer behind the clamp. This overhang should be betweenapproximately inch and /2 inch.

While I have obtained satisfactory results using a single sandwich suchas is illustrated in FIGURES 3 and 4 wherein the two ceramic elements 59and 52 are polarized in the thickness mode and in the same direction andare fed as indicated in FIGURE 4, it is also possible to polarize thetwo ceramic elements in opposite directions in the thickness mode andfeed the two outer electrodes. In such a case, the transducer has itselements driven in series, has an impedance four times that of theparallel feed shown in the figures and requires twice the drivingvoltage.

Improved frequency response is obtained by making the modificationsdiscussed below. For example, some undesired resonances of transducer 36are damped out by removing some of electrode 56 as shown in FIG- URES 5and 10. The response of the transducer is also improved by cutting thingrooves 90, 92 and 4 in the upper surface of ceramic element 50 as shownin FIG- URE 9. I have also found that a single thin groove also producesimprovement in the response of the transducer over that of FIGURES 3 and4.

Similar improvements in frequency response are obtained when using themodifications of FIGURES 6, 7, 8, and 11. FIGURE 6 is a horizontal planview of the embodiment of FIGURE 7. In FIGURE 7 there is shown a secondtransducer 60 of the same shape and material as transducer 36 butshorter in length. Transducer 60 is made up of ceramic elements 62 and64, central brass shim 66 and outer electrodes 68 and 70. Transducer 60is bonded to transducer 36 by means of bonding cement and is fed inparallel therewith as shown in FIGURE 7. I have found that transducer 69should not extend beyond half the free or driving length of transducer36.

In FIGURE 8, there is shown a still further modification of transducer36 for driving loudspeakers of my invention. Strip 8!) is formed ofphenolic, laminated melamine glass or similar material and is bonded tothe upper surface of transducer 36 by means of bonding cement and thetransducer is driven as described heretofore. Generally, strip 80 shouldnot occupy more than half the free end of transducer 36.

In FIGURES 10 and 11 there is shown a still further emobidment oftransducer of my invention. The removal of portions of the electrodes asshown in FIG- URE 5 improves the frequency responses over that of thetransducer of FIGURE 4 and the mounting of a thin, plastic stripedgewise on one surface of the transducer results in additionalimprovement over the embodiment of FIGURE 4. I have found that theunwanted, undesired resonances are damped out when this embodiment isused to drive a loudspeaker diaphragm in loudspeakers of my invention. Ihave obtained excellent results when the length of theelectromechanically inert plastic strip is approximately one half thelength of the driving end of the transducer and the junction of theinert strip and the transducer is parallel to the longitudinal edges ofthe transducer.

It should be noted that I have found that better results are obtained ifthe contact between the transducer and pin 37 is as thin as possible,essentially a knife edge contact, as shown in the figures. V

In operation, audio signal is applied to transformer 46 whose secondaryis connected in push-pull to the grids of tubes 24a and 24b. The platesof tubes 24a and 2412 are also connected in push-pull and B+ is appliedto the plates through the center tap of inductor 28. The output of thepush-pull amplifier is fed to loudspeaker 20 through capacitors 30a and30b. Capacitors 30a and 30b serve to keep the high, positive platevoltage off the transducer of loudspeaker 20. The circuit shown inFIGURE 1 and described herein is one example of an amplifier which maybe used to drive loudspeakers of my invention. Any other amplifier,which produces audio frequency output voltage sufficient to drive thetransducer, may also be employed in carrying out the teachings of myinvention.

Ceramic transducers of my invention deliver relatively high amplitudeswith reasonably flat response over the audible frequency range. Thesetransducers may be connected to a cutting stylus or phonograph pickupneedle in pairs at an angle of and used for stereo recording. A singlesuch transducer may be used for monaural recording. A plurality of suchtransducers may be used for reed relays and similar devices and a singlesuch transducer or a plurality of them may be used as the sensitiveelement in servo valves, meters and other devices requireing areasonably flat frequency response.

While I have disclosed my invention in relation to specific examples andin specific embodiments, I do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of my invention.

Having thus described my invention, I claim:

1. An electromechanical device comprising mounting means, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,mechanical operating means connected to the free end of said transducerfor operation thereby, and means on and adjacent to the free end of thetransducer for damping the same to provide a substantially fiatfrequency response over the audible range.

2. An electromechanical device comprising, an elongatedelectromechanically sensitive ceramic transducer including a pair ofpolarized piezoelectric thin ceramic strips and a conductor stripforming a unitary sandwich and a pair of electrodes on the outersurfaces of said thin ceramic strips, mounting means, means for clampingsaid elongated transducer near one end thereof to the mounting means sothat the active free end of the elongated transducer is approximately 2/2 times as long as the opposite end beyond the point of clamping, meansfor driving said transducer in bending mode including electricalconnections to said conductor strip and electrodes, mechanical operatingmeans connected to the free end of said transducer for operationthereby.

3. An electromechanical device comprising, an elongatedelectromechauically sensitive ceramic transducer including a pair ofpolarized piezoelectric thin ceramic strips and a conductor stripforming a unitary sandwich and a pair of electrodes on the outersurfaces of said thin ceramic strips, mounting means, means for clampingsaid elongated transducer near one end thereof to the mounting means sothat the active free end of the elongated transducer is approximately 2/2 times as long as the opposite end beyond the point of clamping, meansfor driving said transducer in bending mode including electricalconnections to said conductor strip and electrodes, mechanical operatingmeans connected to the free end of said transducer for operationthereby, and means adjacent the free end of the transducer for dampingthe same to provide a substantially flat frequency response over theaudible range.

4. An electromechanical device comprising mounting means, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,mechanical operating means connected to the free end of said transducerfor operation thereby, said electrodes of said elongated transducerterminating short of the free end of the transducer for damping the sameto provide a substantially fiat frequency response over the audiblerange.

5. An electromechanical device comprising mounting means, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,mechanical operating means connected to the free end of said transducerfor operation thereby, and means on and adjacent to the free end of thetransducer for damping the same to provide a substantially flatfrequency response over the audible range, said last mentioned meansincluding an electromechanically inert strip aflixed to said transduceradjacent the free end thereof.

6. An electromechanical device comprising mounting means, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,mechanical operating means connected to the free end of said transducerfor operation thereby, and means on and adjacent to the free end of thetransducer for damping the same to provide a substantially flatfrequency response over the audible range, said last mentioned meansincluding a thin strip of electromechanically inert material afiixed atone of its longer edges to said transducer adjacent the free end thereofand parallel to the longitudinal axis of the transducer.

7. An electromechanical device comprising mounting means, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,mechanical operating means connected to the free end of said transducerfor operation thereby, and means on and adjacent to the free end of thetransducer for damping the same to provide a substantially flatfrequency response over the audible range, said last mentioned meansincluding an electromechanically inert strip aflixed to said transduceradjacent the free end thereof for approximately one half the drivinglength of said transducer.

8. A electromechanical device comprising mounting means, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,mechanical operating means connected to the free end of said transducerfor operation thereby, and means on and adjacent to the free end of thetransducer for damping the same to provide a substantially flatfrequency response over the audible range, said last mentioned meansincluding at least one cut in at least one surface of the transduceradjacent the free end thereof and parallel to the longitudinal axis ofthe transducer.

9. A loudspeaker comprising a frame, a flexible diaphagm aflixed to saidframe, mounting means carried by said frame, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,means for mechanically connecting the free end of said transducer tosaid flexible diaphragm for flexing the same, and means on and adjacentto the free end of the transducer for damping the same to provide asubstantially flat frequency response over the audible range.

10. A loudspeaker comprising a frame, a flexible diaphragm aflixed tosaid frame, mounting means carried by said frame, an elongatedelectromechanically sensitive ceramic transducer including a pair ofpolarized piezoelectric thin ceramic strips and a conductor stripforming a unitary sandwich and a pair of electrodes on the outersurfaces of said thin ceramic strips, means for clamping said elongatedtransducer near one end thereof to the mounting means so that the activefree end of the elongated transducer is approximately 2 /2 times as longas the opposite end beyond the point of clamping, means for driving saidtransducer in bending mode including electrical connections to saidconductor strip and electrodes, means for mechanically connectingthe-free end of said transducer to said flexible diaphragm for flexingthe same.

11. A loudspeaker comprising a frame, a flexible diaphragm aflixed tosaid frame, mounting means carried by said frame, an elongatedelectromechanically sensitive ceramic transducer including a pair ofpolarized piezoelectric thin ceramic strips and a conductor stripforming a unitary sandwich and a pair of electrodes on the outersurfaces of said thin ceramic strips, means for clamping said elongatedtransducer near one end thereof to" the mounting means so that theactive free end of the elongated transducer is approximately 2 /2 timesas long as the opposite end beyond the point of clamping, means fordriving said transducer in bending mode including electrical connectionsto said conductor strip and electrodes, means for mechanicallyconnecting the free end of said transducer to said flexible diaphragmfor flexing the same, and means adjacent the free end of the transducerfor damping the same to provide a substantially flat frequency responseover the audible range.

12. A loudspeaker comprising a frame, a flexible diaphragm affixed tosaid frame, mounting means carried by said frame, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,means for mechanically connecting the free end of said transducer tosaid flexible diaphragm for flexing the same, said electrodes of saidelongated transducer terminating short of the free end of the transducerfor dam-ping the same to provide a substantially flat frequency responseover the audible range.

13. A loudspeaker comprising a frame, a flexible diaphragm aflixed tosaid frame, mounting means carried by said frame, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,means for mechanically connecting the free end of said transducer tosaid flexible diaphragm for flexing the same, and means on and adjacentto the free end of the transducer for damping the same to provide asubstantially flat frequency response over the audible range, said lastmentioned means including an electromechanically inert strip allixed tosaid transducer adjacent the free end thereof.

14. A loudspeaker comprising a frame, a flexible diaphragm aflixed tosaid frame, mounting means carried by said frame, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,means for mechanically connecting the free end of said transducer tosaid flexible diaphragm for flexing the same, and means on and adjacentto the free end of the transducer for damping the same to provide asubstantially flat frequency response over the audible range, said lastmentioned means including a thin strip of electromechanically inertmaterial afiixed at one of its longer edges to said transducer adjacentthe free end thereof and parallel to the longitudinal axis of thetransducer.

15. A loudspeaker comprising a frame, a flexible diaphragm aflixed tosaid frame, mounting means carried by said frame, an elongatedelectromechanically sensitive ceramic transducer clamped adjacent oneend to said mounting means and including a pair of polarizedpiezoelectric thin ceramic strips and a conductor strip forming aunitary sandwich and a pair of electrodes on the outer surfaces of saidthin ceramic strips, means for driving said transducer in bending modeincluding electrical connections to said conductor strip and electrodes,means for mechanically connecting the free end of said transducer tosaid flexible diaphragm for flexing the same, and means on and adjacentto the free end of .the transducer for damping the same to provide asubstantially fiat frequency response over the audible range, said lastmentioned means including an electromechanically inert strip affixed tosaid transducer adjacent the free end thereof for approximately one halfthe driving length of said transducer.

16. A loudspeaker comprising a frame, a flexible diaphragm affixed tosaid frame, mounting means carried by said frame, an elongatedelectromechanically sensitive ceramic transducer clamped adjcent one endto said mounting means and including a pair of polarized piezoelectricthin ceramic strips and a conductor strip forming a unity sandwich and apair of electrodes on the outer surfaces of said thin ceramic strips,means for driving said transducer in bending mode including electricalconnections to said conductor strip and electrodes, means formechanically connecting the free end of said transducer to said flexiblediaphragm for flexing the same, and means on and adjacent to the freeend of the transducer for damping the same to provide a substantiallyflat frequency response over the audible range, said last mentionedmeans including at least one cut in at least one surface of thetransducer adjacent the free end thereof and parallel to thelongitudinal axis of the transducer.

References Cited in the file of this patent UNITED STATES PATENTS2,045,403 Nicholides June 23, 1936 2,166,326 Riesz July 18, 19392,223,537 Sykes Dec. 3, 1940 2,269,403 Williams Jan. 6, 1942 2,352,311Di Toro June 27, 1944 2,510,811 Gale June 6, 1950 2,587,684 Bauer Mar.4, 1952 2,640,165 Howatt May 26, 1953 FOREIGN PATENTS 698,989 GreatBritain Oct. 28, 1953

1. AN ELECTROMCHANICAL DEVICE COMPRISING MOUNTING MEANS, AN ELONGATEDELECTROMECHANICALLY SENSITIVE CERAMIC TRANSDUCER CLAMPED ADJACENT ONEEND TO SAID MOUNTING MEANS AND INCLUDING A PAIR OF POLATIZEDPIEZOELECTRIC THIN CERAMIC STRIPS AND A CONDUCTOR STRIP FORMING AUNITARY SANDWICH AND A PAIR OF ELECTRODES ON THE OUTER SURFACES OF SAIDTHIN CERAMIC STRIPS, MEANS FOR DRIVING SAID TRANSDUCER IN BENDING MODEINCLUDING ELECTRICAL CONNECTIONS TO SAID CONDUCTOR STRIP AND ELECTRODES,MECHANICAL OPERATING MEANS CONNECTED TO THE FREE END OF SAID TRANSDUCERFOR OPERATION THEREBY, AND MEANS ON ADJACENT TO THE FREE END OF THETRANSDUCER FOR DAMPING THE SAME TO PROVIDE A SUBSTANTIALLY FLATFREQUENCY RESPONSE OVER THE AUDIBLE RANGE.